Microwave response of single crystal YBa₂Cu₃O₇–δ films as a probe for pairing symmetry

• Published in: Физика низких температур
• Date: 2006
• Main Authors: Pan, V.M., Kalenyuk, O.A., Kasatkin, O.L., Komashko, V.A., Ivanyuta, O.M., Melkov, G.A.
• Format: Article
• Language: English
• Published: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2006
• Subjects: Experimental Methods and Applications
• Online Access: https://nasplib.isofts.kiev.ua/handle/123456789/120199
• Journal Title: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Cite this: Microwave response of single crystal YBa₂Cu₃O₇–δ films as a probe for pairing symmetry / V.M. Pan, O.A. Kalenyuk, O.L. Kasatkin, V.A. Komashko, O.M. Ivanyuta, G.A. Melkov // Физика низких температур. — 2006. — Т. 32, № 4-5. — С. 651–660. — Бібліогр.: 50 назв. — англ.

Temperature dependences of the microwave surface impedance, Zs(T), are measured in the
 c-axis oriented single-crystal high-Tc superconducting cuprate YBa₂Cu₃O₇₋δ (YBCO) thin films
 deposited by the off-axis dc magnetron sputtering onto CeO₂-buffered single-crystal sapphire
 substrates (film thickness is d ≈ 150, 300, 480 nm). Measurements are performed by a use of the
 coplanar resonator as well as the end-plate cylindrical cavity resonator techniques at a number of
 several discrete frequencies within the range of 5–134 GHz. The measurements have revealed
 unexpected peculiarities on the Zs(T)-dependences for the most perfect films under study. The
 peculiarities appear to be most strongly pronounced on the temperature dependences of the film
 surface resistance Rs(T) = Re {Zs(T)}. The most important features of the unusual surface
 resistance behavior are: (i) the temperature dependence Rs(T) of YBCO films under study at low
 temperatures obeys the exponential law: Rs(T) = Rres + R₀ exp [–∆s/T] with the small energy gap
 ∆s (∆s 0.5Tc at f = 5 GHz); (ii) the most perfect films reveal a distinct two-peak structure of the
 Rs(T) dependence with peaks positioned at 27–30 K and 48–51 K, while such peaks are not
 observed in less perfect films. The peaks are mostly pronounced at moderate (e.g. 34 GHz)
 frequencies and gradually disappear both at higher and lower frequencies, while their temperature
 positions remain unchanged. These features of perfect single-crystalline YBCO films are believed
 to reveal their intrinsic electron properties. Taking into account the possibility of a mixed
 (s+id)-type pairing symmetry as well as a significant role of extended out-of-plane crystal defects
 (such as dislocation lines or twin planes) in Bogolyubov’s quasiparticle scattering within the most
 perfect YBCO films, one can suggest a consistent explanation for the anomalies observed in the
 Zs(T) behavior.